sorry, I thought u just need two vertical walls. I'm not sure about the hole
with four vertical walls

  Regards

  guocheng shao

Sudarshan Hegde  wrote:
  Hi Shao
The paper was helpful regarding the methods dealing with perfect aligning.
Thanks a lot.
This paper discusses deep but long channels.
In principle, (given that the alignment is perfect) is it possible to get
vertical holes. i.e., four vertical walls ?
Thanks and regards
Sudarshan Hegde